Both nuclear progesterone receptors (nPRs), PR-A and PR-B, are expressed in human luteal cells. Further, progesterone (P4) inhibits and the nPR antagonist, RU486, induces human luteal cell apoptosis (i.e., programmed cell death). These observations suggest that P4 mediates its antiapoptotic action by activating the nPRs. However, recent studies have shown that P4 modulates luteal cell function by both genomic and non-genomic mechanisms. Moreover, several membrane receptors, or mediators of P4's action, are expressed by luteal cells. Since the precise regulation of luteal cell viability is required for the reproductive process, it is essential that we determine which receptor, or receptors, mediates P4's antiapoptotic action in human luteal cells. We should not accept the concept that P4 mediates its antiapoptotic action exclusively through the nPRs, since this assumption is based solely on nPR expression and pharmacological studies. Therefore, we will use genetic approaches to modulate the levels of nPRs in cultured human luteal cells and then assess P4's ability to prevent luteal cell apoptosis. We propose the following three specific aims: 1) to characterize human luteal cell differentiation and regression in vitro in terms of P4 secretion and expression of nPR as well as other potential mediators of P4's action; 2) to correlate the ability of P4 to maintain the viability of human luteal cells with the expression of the nPRs and other P4 mediators; and 3) to determine the effect of specific ablation and over expression of the nPRs on the ability of P4 to promote luteal cell viability. If the studies indicate that P4's antiapoptotic activity is not exclusively mediated by the nPRs, then one or more of the other potential P4 mediators could be involved in transducing P4's antiapoptotic action. If so, this could open up new areas of pharmacology that would be directed toward inhibiting or enhancing the action of these other P4 mediators. Since the structures of three of these candidate proteins are very different from that of the nPRs, drugs could potentially be developed that influence their action without interfering with the action of the nPRs. Such selective manipulation of the P4's actions could have far reaching effects on the treatment for infertility, contraception and certain types of cancers. [unreadable] [unreadable]